Cellulose, in general, is an ubiquitous polysaccharide present in higher plants, such as trees, and functions as the structural material of the cell membranes and is a major contributor to the shape and rigidity of such plants. Such cellulose is a high molecular weight, largely linear compound composed of D glucose units joined by .beta. 1,4 glusodidic bonds. Cellulose is a naturally occurring polymer, like, for example, a starch, but unlike starch which is a reserve polymer of glucose with predominately .alpha. 1,4 glucosidic bond, cellulose is not digested by most animals, including humans, to a glucose constituent. As a result thereof, cellulose, since it is non-nutritional for human use, the sources contemplated for the production of cellulose has been a problem.
The commercial source heretofore employed for the production of a relatively pure cellulose has been from higher plants and has principally been directed at producing a fibrous cellulose for use in the production of felted cellulosic products, such as, for example, paper. To a lesser extent, cellulose has also been produced from higher plants for use in the preparation of cellulosic polymers which are employed in the textile industry in the production of explosives and in various other industrial products.
The primary source of cellulose for use in the production of paper is wood, which contains about 50% cellulose, from which such wood the cellulose can economically be separated in relatively pure form, with the cellulose possessing excellent color and having a satisfactory fiber length and strength. In the other industrial operations employing cellulose, such cellulose will require a higher degree of purity and thus must employ highly purified wood or treated cotton linters as the raw material from which the cellulose will be extracted. Other sources of cellulose that have been contemplated heretofore in an effort to offset increased costs of wood and cotton linters have included many other woody or fibrous plant materials, such as, corn stalks, rice, and like straw material, hemp, bagasse, and other materials of a like nature.
In recent years, however, highly purified cellulose in a finely divided or powdered form has been produced and proposed for use as a material suitable for human consumption or human use. Such uses have included the use of the cellulose as an excipient in pharmaceutical tableting, as an inert filler in various products, and as a filter aid in the purification of various liquid compounds in the processing thereof. Such cellulose has also been proposed more recently as a component for use in various foodstuffs, such as, for example, a bulking agent in bread. In this particular use, the cellulose functions to impart fiber or roughage to the bread, thus enhancing the dietary characteristics of the bread. Such use in bread products also functions to reduce the overall calorie content of the bread without reducing the volume of the product. For such use as a bread additive, the cellulose employed heretofore has been quite expensive since the cellulose costs two to five times as much as the starch and sugar, which have been employed heretofore for similar purposes in bread.
In an effort to provide highly purified cellulose which will satisfy the requirements of human consumption and use, deciduous woods, to wit, hard woods, have been employed as the feedstock for the production of the powdered cellulose, since such woods produce a finer cellulose fiber. In the production of cellulose fibers from such woods, the barked wood is chipped into small pieces and thereafter cooked and digested at an elevated temperature with a mixture of sodium hydroxide and sodium sulfite solution to dissolve and remove the largely ligneous cementum of the wood. This operation produces a pulped cellulose material which is subjected to a bleaching operation and thereafter the cellulose is extracted by means of a sodium hydroxide solution treatment in a multi-staged process, which is necessary to get the purity required. This procedure is essentially a paper making operation and the resulting end product is then ground to produce the cellulose powder sought. The chopping and grinding of the paper product to produce the cellulose powder is a tedious and difficult procedure. It is to be noted that equally pure cellulose obtained from more economical soft wood cellulosic material, being coarser, cannot conveniently be powdered to the desired fineness.
Powdered cellulose derived from hard wood possesses a fundamental disadvantage as a food component, even though its use is indicated both physiologically and technically to be desirable. For example, powdered cellulose is included in the Food Chemicals Codex II NAS-NRC (1972). This disadvantage is due to the fact that the source of the cellulose, to wit, hard wood, does not connote edibility.
Another cellulose contemplated for use as a food component is microcrystalline cellulose, which is a highly purified non-fibrous cellulose. The cellulose is prepared from purified cellulose obtained from wood or cotton sources by a process of caustic solution and reprecipitation which somewhat reduces the native molecular weight and yields a high purity versatile product. The product so produced is comparatively expensive and has found limited uses in foods, but has been found to be an excellent excipient for drug use. It is listed in the National Formulary and in the Food Chemicals Codex II.
In an effort to eliminate the foregoing disadvantages, a principal objective of the present invention is directed to the production of a purified powdered cellulose from a source having a definite connotation of edibility. Another object is to provide a process of sufficient simplicity that can be utilized with an existing food processing factory, such as, for example, a soybean processing plant or a wet corn processing plant and using as the raw material source for the cellulose the fibrous by-product of the mill, which would normally be discarded. A further object of the present invention is to provide a process for producing a purified cellulose which, by reason of its fine and short fiber character, is inferior for use in paper manufacture but superior for the production of powdered cellulose suitable for use as a food or drug compound. Still another object of the present invention is to provide a powdered cellulose which is not only economically superior to the cellulose derived from wood, but also is functionally superior for food and drug applications because of its enhanced surface area.